Frequency-dependent Thermal Response of the Charge System and Restricted Sum Rules in La(2-x)Sr(x)CuO(4)

Abstract

By using new and previous measurements of the $ab$-plane conductivity ${\sigma }_1^{ab}(\omega ,T)$ of La${}_{2-x}$Sr${}_x$CuO${}_4$ (LSCO) it is shown that the spectral weight $W={\int }_0^{\Omega }{\sigma }_1^{ab}(\omega ,T)d\omega$ obeys the same law $W=W_0-B(\Omega )T^2$ which holds for a conventional metal like gold, for $\Omega$'s below the plasma frequency. However $B(\Omega )$, which measures the "thermal response" of the charge system, in LSCO exhibits a peculiar behavior which points towards correlation effects. In terms of hopping models, $B(\Omega )$ is directly related to an energy scale $t_T$, smaller by one order of magnitude than the full bandwidth $t_0\sim W_0$.

4 pages with 3 figs